A general difficulty with medical devices which come into contact with infection-sensitive areas of the body is that they may, themselves, introduce infection into the body or serve as a conduit for the introduction of infection over time. These infection-sensitive areas include body orifices and wounds. Intrusive medical devices such as central venous catheters (CVCs), urinary catheters and endotracheal catheters may introduce infection into hospitalized patients when used since the devices are subject to microbial colonization.
The most common organisms causing these infectious complications are Staphylococcus epidermidis and Staphylococcus aureus. In the case of vascular catheters, these two organisms account for almost 70-80% of all infectious organisms, with Staphylococcus epidermidis being the most common organism. Candida albicans, a fungal agent, account for about 10-15% of catheter infections. A number of studies have revealed that organisms such as Staphylococcus epidermidis send projections into small defects in the polypropylene material, which is used in catheters. Protection against infection is desirable at and around the catheter insertion point to limit entrance of organisms into the intercutaneous tunnel.
A related problem lies within non-intrusive external medical aids such as bandages, gauze pads and other dressings that are placed in contact with wounds on the body during healing. These dressings must be changed regularly and/or have antibiotic medications added to them to resist infection of the wound. In many cases in which the patient's tissue is extremely sensitive, such as wound dressings for burns or ulcers, it would be advantageous to avoid the many changes. Even with frequent and regular dressing changes, a large number of site infections can be expected to occur.
The use of antimicrobial creams or other coatings, such as chlorhexidine, may not provide an effective countermeasure to catheter-related or dressing-related infections. The coatings may themselves be contaminated or be improperly or incompletely applied over the surface of the item rendering the coating ineffective. In addition, the antimicrobial effect: of these coatings is only temporary and has the potential to build resistance by the microbes to the particular antimicrobial agent used.
Heavy metals, particularly gold, silver, and copper are known to exert, in the form of metal ions, an antimicrobial effect known as oligodynamic activity to counter infections. A number of devices have been created which employ such materials to obtain an antimicrobial effect.
A cuff has been designed which is composed of collagen impregnated with silver ions, which may be placed around a central venous catheter prior to catheter insertion and positioned subcutaneously after catheter placement. The collagen induces tissue ingrowth which seals the catheter track, and the antimicrobial activity of the silver serves as an additional barrier to organisms migrating into the catheter track. Due to the collagen composition, the cuff itself actually dissolves away after a short period of time.
A urinary catheter device is also known which includes electrodes originating at the proximal end of the catheter and running along the internal length of the catheter lumen to the catheter's distal end. The catheter is adapted to accommodate current from a constant current source and transmit the current to the internal electrodes. In one embodiment, the electrodes may exit the tubular wall of the catheter near a distal end collection orifice thus exposing their surfaces to the inner lumen of the catheter. The electrodes are preferably made of a heavy metal and are ionized by the constant current source to provide for antimicrobial action.
Another bacterial barrier is known which may be used with indwelling catheters and similar medical devices which is designed to produce a circumferential zone of bacterial inhibition just within the body opening when the device is installed. The barrier is in the form of a fixed or detachable thin band, stretchable or shrinkable ring, or plastic nonconductive tape having a continuous strip of oligodynamic metal, such as silver, zinc, copper or aluminum; a more noble metal, such as platinum or gold; and a self contained current source.